BASED ON Moffette, F., Alix-Garcia, J., Shea, K. & Pickens, A. H. Nat. Clim. Change https://doi.org/10.1038/s41558-020-00956-w (2021).

## The policy problem

Deforestation in the tropics has major effects on climate change and biodiversity loss. Furthermore, policies that limit deforestation are more cost effective than interventions to restore landscapes after conversion for agriculture or other uses. Many strategies are available to reduce deforestation — creating protected areas, payments for ecosystem services, supply-chain agreements — all of which require that forests be monitored. Until recently, annual deforestation maps released the following year often provided the best monitoring data available. Deforestation rates are generally highest in countries with limited resources to create effective monitoring systems, so making low-cost technologies available may be an important way to support effective policies that aim to prevent deforestation. Using weekly near-real-time deforestation alerts freely available via a platform unaffiliated with any governmental intervention and accessible from anywhere on the globe could have an impact on land-use trends and inform the design of more effective anti-deforestation strategies.

## The findings

Use of the GLAD (global land analysis and discovery) alerts, through subscription to Global Forest Watch, decreased the probability of deforestation in Africa by 18% within the first two years relative to the average 2011–2016 levels. The simple availability of the alerts did not significantly impact deforestation, and we found no effect on other continents. Effects in Africa were driven by subscriptions within protected areas and logging concessions, which suggests that the alerts were used to fight illegal deforestation. Using the social cost of carbon, we estimate the value of the alert system to be in the range of US$149–$696 million. However, the benefits are probably greater since co-benefits such as biodiversity are not included and the effectiveness of using the alerts may be increasing over time. Alert systems are likely to be effective in other regions as long as they provide earlier or more accessible reports of forest loss and policies designed to reduce deforestation are enforced.